diff --git a/.eslintrc b/.eslintrc
index ef0fe2cd3..37f9f057b 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -179,6 +179,10 @@
         "selector": "CallExpression[callee.name='assert'][arguments.length!=2]",
         "message": "`assert()` must always be invoked with two arguments.",
       },
+      {
+        "selector": "CallExpression[callee.name='isCmd'][arguments.length<2]",
+        "message": "Use `instanceof Cmd` rather than `isCmd()` with one argument.",
+      },
       {
         "selector": "NewExpression[callee.name='Cmd']",
         "message": "Use `Cmd.get()` rather than `new Cmd()`.",
diff --git a/src/core/cmap.js b/src/core/cmap.js
index 9c0c373ff..ab2228a9e 100644
--- a/src/core/cmap.js
+++ b/src/core/cmap.js
@@ -20,7 +20,7 @@ import {
   unreachable,
   warn,
 } from "../shared/util.js";
-import { EOF, isCmd, isName } from "./primitives.js";
+import { Cmd, EOF, isCmd, isName } from "./primitives.js";
 import { BaseStream } from "./base_stream.js";
 import { Lexer } from "./parser.js";
 import { MissingDataException } from "./core_utils.js";
@@ -920,7 +920,7 @@ const CMapFactory = (function CMapFactoryClosure() {
             parseCMapName(cMap, lexer);
           }
           previous = obj;
-        } else if (isCmd(obj)) {
+        } else if (obj instanceof Cmd) {
           switch (obj.cmd) {
             case "endcmap":
               break objLoop;
diff --git a/test/unit/primitives_spec.js b/test/unit/primitives_spec.js
index fbcdaa62f..6604517df 100644
--- a/test/unit/primitives_spec.js
+++ b/test/unit/primitives_spec.js
@@ -496,6 +496,8 @@ describe("primitives", function () {
   });
 
   describe("isCmd", function () {
+    /* eslint-disable no-restricted-syntax */
+
     it("handles non-commands", function () {
       const nonCmd = {};
       expect(isCmd(nonCmd)).toEqual(false);
@@ -511,6 +513,8 @@ describe("primitives", function () {
       expect(isCmd(cmd, "BT")).toEqual(true);
       expect(isCmd(cmd, "ET")).toEqual(false);
     });
+
+    /* eslint-enable no-restricted-syntax */
   });
 
   describe("isDict", function () {